The present invention relates generally to film cooled combustor liners for use in a gas turbine engine and, in particular, to such combustor liners including a multihole patch of cooling holes formed in regions thereof which experience an undesirable thermal gradient.
Combustor liners are generally used in the combustion section of a gas turbine engine located between the compressor and turbine sections of the engine, although such liners may also be used in the exhaust sections of aircraft engines that employ augmenters. Combustors generally include an exterior casing and an interior combustor where fuel is burned to produce a hot gas at an intensely high temperature (e.g., 3000° F. or even higher). To prevent this intense heat from damaging the combustor case and the surrounding engine before it exits to a turbine, a heat shield or combustor liner is provided in the interior of the combustor.
Various liner designs have been disclosed in the art having different types of cooling schemes. One example of liner design includes a plurality of cooling slots formed therein by a plurality of cooling nuggets or the like (e.g., U.S. Patent), where a film of cooling air is provided along the hot side of the liner. Another liner design has been developed, as disclosed in U.S. Pat. No. 5,181,379 to Wakeman et al., U.S. Pat. No. 5,233,828 to Napoli, and U.S. Pat. No. 5,465,572 to Nicoll et al., where a plurality of cooling holes have been formed in an annular one-piece liner to provide film cooling along the hot side of the liner. Further, a combination of multihole cooling and slot-type cooling has been described in U.S. Pat. No. 5,483,794 to Nicoll et al., U.S. Pat. No. 5,279,127 to Napoli, U.S. Pat. No. 5,465,572 to Nicoll et al., and U.S. Pat. No. 4,833,881 to Vdoviak et al.
Each of the aforementioned patents is primarily concerned with various ways in which to provide the desired cooling film for the liner while oftentimes attempting to minimize the amount of cooling air required therefor. Thus, the designs incorporating both multihole cooling and slot cooling involve a distinct separation (i.e., where the slot cooling is utilized in only a first or upstream portion of the liner and the multihole cooling is utilized in only a second or downstream portion of the liner as in the '881 patent), a single cooling slot being provided at an upstream end of the liner in order to assist in starting the cooling film of an otherwise multihole cooled liner as in the '127 patent, or a plurality of spaced cooling slots being provided upstream of separate multihole patterns extending circumferentially around the liner as in the '572 and '794 patents. None of these patents, however, disclose the use of discrete patches of multiholes being provided to augment the cooling film provided by cooling slots on nuggeted liners.
It will also be noted that U.S. Pat. No. 6,205,789 to Patterson et al. discloses a multihole film cooled combustor liner which includes a first group of cooling holes generally disposed therein and a second group of more densely spaced cooling holes incorporated with the first cooling hole group. This second group of cooling holes is provided at various locations of the liner where the cooling film is degraded, such as those regions subjected to swirl impingement or located immediately downstream of a large opening. While the second cooling hole group is defined within certain regions, it must be compatible with the first cooling hole group by maintaining consistent axial spacing and hole size. This limits the flexibility of the pattern to address the specific thermal gradients experienced by the liner.
It will be appreciated that an exemplary double annular combustor includes what is known as a co-rotating, no venturi (CONOVEN) swirler in the main dome. While this combustor is able to minimize emissions, it has been found that an extraordinary amount of hot gases impinge on the inner liner thereof. Such hot gas impingement has been found to produce early oxidation of the forward liner panels, which results in reduced life and combustor burn through in severe cases. In order to solve this problem, additional air is required to cool the distressed panel. Additional cooling flow has been gained in machined slot liners by increasing the size and/or number of the cooling holes feeding the cooling slot. This method has been effective in those cases where there is sufficient space to drill the required number/size of the holes for decreasing the panel temperature to an acceptable level, but the required space is not available in every instance.
Thus, it would be desirable for a combustor liner to be developed for use with a gas turbine engine combustor which provides additional cooling in discrete regions of the liner as required by the thermal gradients experienced. It would also be desirable for such multihole cooling patches to be utilized with liners having either slot cooling or multihole cooling.